I can never understand the fascination people have with high ISO performance. No camera, even the low light geniuses like the D700 and D3 gets anywhere near its best performance more than 2, maybe 3, stops above its "base" iso. So with a base ISO of (say) 200, you will get your very best sharpness, colour, DR, noise etc etc at 200. This will hold up really well at 400, be pretty close at 800 and be noticeably different though probably still pretty good at 1600. Beyond here the quality fall off is obvious and clearly something you would want to avoid.
And this isnt a Sony thing, or a Nikon thing or a Canon thing - its a physics thing. Look at test photos from any camera and compare its output at ISO 100/200 to what it gets at 800/1600. Its obvious, while the high iso shots might be useable, side by side with the ISO 100/200 they will suck.
Thats probably why as I look through the 20000 odd photo's in my catalog, 95.2% of them are taken at ISO 800 or lower. Another 4.4% are at ISO 1600. And yes, do the maths and you'll see 0.4% of my photos are taken at ISO 3200 or higher.
So frankly I dont really care about high iso performance and whats more, given that most people I speak to have similar sorts of usage patterns I dont understand why most people seem to.